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09 yz450 question

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hi im new to this form and would like to say hi

I just bought a new yz450 2009 and i haven't broke it in yet. i started it up and it was back firing when i let off the throttle at 1/4 of a throttle

my question is? is that common or is there something wrong . thanks

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The pilot jet is probably a little lean, since the weather is a little cooler now than the conditions it is jetted for. Try a larger pilot jet.

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The pilot jet is probably a little lean, since the weather is a little cooler now than the conditions it is jetted for. Try a larger pilot jet.

This is most likely true. You can try adjusting the fuel screw first but don't make any adjustments until the bike is fully warmed up.

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Yep...turn the fuel screw all the way in counting the number of full turns...then turn it back out past where it was but no further than 3 full turns to try to make the backfiring go away...if it still does it after this adjustment, then go to a one size bigger pilot jet. I am near sea-level and didnt need a larger pilot jet...just some fuel screw adjustments. You should buy an aftermarket fuel screw to make the adjustments easier.

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Be sure that you check for exhaust leaks at both ends of the header before playing with the screw. If the backfire is caused by a leak, you'll end up with a bike that idles poorly, fouls plugs, starts hard, and dies when the throttle is chopped. Just sayin'.

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I have the exact problem. I have an 08 stock tires and eavrything idle jet all the way. Iv had it a month and it barly ran decent. Don't ride it like that! Iv had mine a week with the jet worked and it's awsom. Easy

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I have the exact problem. I have an 08 stock tires and eavrything idle jet all the way. Iv had it a month and it barly ran decent. Don't ride it like that! Iv had mine a week with the jet worked and it's awsom. Easy

huh??? :banana:

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Be sure that you check for exhaust leaks at both ends of the header before playing with the screw. If the backfire is caused by a leak, you'll end up with a bike that idles poorly, fouls plugs, starts hard, and dies when the throttle is chopped. Just sayin'.

How do you check it? is it by plugging the end of the exhaust?

If so what should I look for? will the bike stop running?

THX

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thanks for the help ill keep you posted i just bought a fuel mix screw today and ill ride tomorrow:thumbsup:

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How do you check it? is it by plugging the end of the exhaust?

If so what should I look for? will the bike stop running?

THX

You can do it that way, but get it running first. Any leaks should be obvious. But you can also start by seeing if the clamps and flange plate are tight.

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